Systems, including Heating, Ventilating and Air-Conditioning (HVAC) systems, are implemented with one or more controlled devices that are operated for controlling and regulating the flow or movement of fluids, such as air, gases or liquids, within the system. The controlled devices include valves and dampers, which are operated using one or more actuating devices. Typically, an actuating device, simply referred as an actuator, includes a prime mover, such as a motor, which is operated to open and/or close one or more valves or dampers. The degree of opening or closing of the valves or dampers is controlled for the regulation of fluid flow within the system.
In some systems, in case of an emergency, such as fire, smoke, frosting, leakage, or an undesirable power failure, it may be required that the one or more controlled devices in the system are moved to a predefined safe position. The predefined safe position may be an open position or a closed position of the controlled device, which may be necessary to attain for the safety of the system in the emergency or power failure situations. Such a predefined safe position of the controlled device is typically referred to as a fail-safe position.
For moving the controlled device to a fail-safe position, the system is implemented with a fail-safe operation. The fail-safe operation may be achieved through a fail-safe actuating system. The fail-safe actuating system may either be integrated with the actuating device operating the controlled device, or be provided as a separate actuating system. The fail-safe operation or fail-safe actuating system is an essential aspect in systems involving flow or movement of fluids and, thus, it is important to have a simple, cost-effective and efficient fail-safe operation or fail-safe actuating system in such systems.